This invention generally relates to an acoustic liner. More particularly, this invention relates to an acoustic liner for minimizing reflection of sound from the acoustic liner face.
Conventional nacelle liners include a noise attenuating structure covered by a face sheet including a plurality of openings. The openings communicate noise and acoustic energy through to the noise attenuating structure where the acoustic energy is dissipated. The face sheet includes an open area provided by the plurality of openings that is generally less than 20% of the total area of the face sheet. The open area provided by openings within the face sheet is configured to attenuate the most undesirable noise frequencies. The limited and tailored open area prevents sound energy of some frequencies from being dissipated and instead reflects that sound energy back into the nacelle. Greater open area can provide improvements to the range of noise frequencies that can be attenuated.
Disadvantageously, there is a practical limit to the number and size of the openings that can be provided within a face sheet. Further, although possible to tune the liner to attenuate noise of certain frequencies, such tailoring results in a limit to the range of frequencies that can be effectively attenuated. Although increases in open area can increase the range of sound frequencies that can be attenuated, the number and size of openings should also provide desired manufacturing efficiencies, while being balanced against the open area requirements.
Accordingly, it is desirable to develop and design a liner assembly with improved noise attenuation properties that can attenuate a broad range of noise frequencies.